1. Field of the Invention
The present invention relates to an apparatus which performs a plasma process on a target substrate by using plasma in, e.g., a semiconductor processing system. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In general, in the manufacture of a semiconductor device, various processes, such as film formation, annealing, etching, oxidation and diffusion, and the like, are performed. Most of these processes are performed in a plasma processing apparatus using radio-frequency (RF) power.
For example, in a parallel-plate plasma processing apparatus, a semiconductor wafer is placed on a lower electrode also serving as a susceptor. RF power is applied across the lower electrode and an upper electrode opposing it, to generate plasma. Various processes, such as film formation and etching, are performed with the plasma.
To increase the yield of the products manufactured from a semiconductor wafer, the planar uniformity of the plasma process for the wafer must be maintained high. In this case, the plasma process uniformity for the semiconductor wafer largely depends on the state of the plasma generated in the process chamber. Hence, conventionally, to optimize the plasma state, the pressure or temperature in the process chamber during the process is adjusted. Also, the gas ratio of the various gases supplied into the process chamber is adjusted. Alternatively, the gap between the upper and lower electrodes is finely adjusted.
In the conventional apparatus, a structure that can adjust the gap between the upper and lower electrodes tends to be employed, because this structure is particularly effective in controlling the plasma state. For example, an elevating mechanism for vertically moving the lower electrode is provided at the bottom of the process chamber, so that the lower electrode can be moved vertically. The lower electrode is vertically moved when necessary by using the elevating mechanism, and the gap between the lower and upper electrodes is adjusted.
In the plasma processing apparatus as described above in which the electrode can be vertically moved, the plasma can be maintained in a good state regardless of the process conditions and the condition of the apparatus itself. However, for example, the lower electrode itself must be able to vertically move while maintaining the airtight state of the interior of the apparatus. Also, the elevating mechanism and a motor for vertically moving the lower electrode must be provided. Consequently, not only the apparatus size becomes large, but also the cost increases. As the size of the apparatus itself becomes large, the space needed to install the apparatus, i.e., the footprint, also increases undesirably.